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LM34919 Ultra Small 40V, 600 mA Constant On-Time Buck Switching Regulator
June 2, 2008
LM34919 Ultra Small 40V, 600 mA Constant On-Time Buck Switching Regulator
General Description
The LM34919 Step Down Switching Regulator features all of the functions needed to implement a low cost, efficient, buck bias regulator capable of supplying 0.6A to the load. This buck regulator contains an N-Channel Buck Switch, and is available in a micro SMD package. The constant on-time feedback regulation scheme requires no loop compensation, results in fast load transient response, and simplifies circuit implementation. The operating frequency remains constant with line and load variations due to the inverse relationship between the input voltage and the on-time. The valley current limit results in a smooth transition from constant voltage to constant current mode when current limit is detected, reducing the frequency and output voltage, without the use of foldback. Additional features include: VCC under-voltage lockout, thermal shutdown, gate drive under-voltage lockout, and maximum duty cycle limiter.
Features
■ Integrated N-Channel buck switch ■ Integrated start-up regulator ■ Input Voltage Range: 8V to 40V
■ No loop compensation required ■ Ultra-Fast transient response ■ Operating frequency remains constant with load current
and input voltage
■ Maximum switching frequency: 2.0 MHz ■ Maximum Duty Cycle Limited During Start-Up ■ Adjustable output voltage ■ Valley Current Limit At 0.64A ■ Precision internal reference ■ Low bias current ■ Highly efficient operation ■ Thermal shutdown
Typical Applications
■ High Efficiency Point-Of-Load (POL) Regulator ■ Non-Isolated Telecommunication Buck Regulator ■ Secondary High Voltage Post Regulator
Package
■ micro SMD
Basic Step Down Regulator
© 2008 National Semiconductor Corporation 300044
30004431
www.national.com
LM34919
Connection Diagrams
Bump Side
30004402
Top View
30004433
Ordering Information
Order Number LM34919TL
LM34919TLX
Package Type 10-Bump micro SMD
10-Bump micro SMD
NSC Package Drawing TLP10A1A
TLP10A1A
Junction Temperature Range −40°C to + 125°C
−40°C to + 125°C
Supplied As
250 Units on Tape and Reel
3000 Units on Tape and Reel
www.national.com
2
LM34919
Pin Descriptions
Pin Number A1
Name RON/SD
Description On-time control and shutdown
A2
RTN
Circuit Ground
A3 FB Feedback input from the regulated output
B1
SGND
Sense Ground
B3 SS Softstart
C1
ISEN
Current sense
C3
VCC
Output from the startup regulator
D1 VIN Input supply voltage D2 SW Switching Node
D3 BST Boost pin for bootstrap capacitor
Application Information
An external resistor from VIN to this pin sets the buck switch on-time. Grounding this pin shuts down the regulator.
Ground for all internal circuitry other than the current limit detection.
Internally connected to the regulation and over-voltage comparators. The regulation level is 2.5V.
Re-circulating current flows into this pin to the current sense resi.